Insulating glass units (IGUs or IG units) are known in the art. See, for example, U.S. Pat. Nos. 6,632,491; 6,014,872; 5,800,933; 5,784,853; and 5,514,476, and also U.S. Publication No. 2007/0128449, the entire contents of each of which are hereby incorporated herein by reference.
Insulating glass units generally include two panes, sheets, substrates, or lites of glass in substantially parallel spaced apart relation to one another, with an optionally gas filled pocket therebetween. As shown in FIG. 1, first and second substrates 10a and 10b are sealed together through the use of seals/spacers 12 around the edges of the two substrates 10a and 10b. The sealing components in a conventional IG unit may include both a sealer component and a spacer component. The spacer component may act to support the weight of the substrates by holding them apart (and thus forming a gap therebetween).
The seals sometimes may act to hold the substrates together. In certain instances, these edge seals may be hermetic seals. The use of hermetic seals may allow for the gap between the substrates to be filled with a gas. In certain conventional IG units, a desiccant may be exposed to the interior gap between the substrates. The desiccant may act to keep this interior gap dry (e.g., decrease condensation).
Once sealed, the IGU is formed and may be installed in a commercial, residential, or other setting, e.g., as an energy saving window. In comparison to a single paned window, a standard double paned window may have an R-value more than 2. IG units may have yet higher R-values. Additional techniques may be used to yet further increase the R-value of a window. On conventional technique involves disposing a low-E coating 14 (e.g., as shown in FIG. 1) to a surface of one of the substrates. Another technique involves tinting the glass substrates. Some techniques may be applied to decrease the heat transference over the gap between the two substrates 10, for example, by creating a vacuum or near-vacuum between the two panes of glass or filling the gap with an inert gas such as argon. As is known, R-values are measures of thermal resistance and may be obtained by for an entire section of material by dividing the unit thermal resistance by the cross-sectional area of the depth of the material or assembly. The overall heat transfer coefficient, or U-value, is the inverse of the R-value, and describes how well a building element conducts heat.
New techniques of reducing heat transference are continually sought after in order to improve, for example, the energy efficiency of windows. Also, new techniques in making IG units are also continuously sought after for reducing the overall cost of the IG unit. Higher R-values and thus lower U-values typically correspond to more energy efficient materials. Thus, it will be appreciated that when designing more energy efficient windows, it would be desirable to provide reduced U-values to correspondingly reduce heat losses through the window from inside to outside (in cold regions). In addition, it also would be desirable to provide a high and neutral visible transmission (Tvis) and a high solar heat gain (solar factor or g-value), thereby making it possible for solar radiation to pass through the window to heat up the room indoor (e.g., on cold days).
Heat losses caused by convection and thermal conduction may be reduced by optimizing the gas and the spacer width. However, a significant part of thermal losses is caused by heat radiation. To reduce this kind of loss, the emissivity of at least one surface of the IGU has to be reduced, which can be achieved by low-E coatings, as alluded to above. Because these coatings in general are very sensitive to humidity and other environmental conditions, low-E coatings typically are applied to at least one surface oriented towards the sealed spacer filled with the noble gas.
Unfortunately, for physical reasons, it is difficult to lower the U-value while keeping the visible transmission and g-value at their original levels. For example, when attempting to lower the U-value by coating more surfaces or by modifying the coating, visible transmission and g-values are typically decreased. Typical performance data for double glaze IGUs is shown in the table below. The data in the table below has been simulated for IGUs including two sheets of 4 mm thick float glass, 90% argon filled cavities spaced apart with 16 mm spacers, and having their third surface coated with a low-E coating. As can be seen from the table below, it is possible to achieve an emissivity of 2%, which leads to a U-value achievable by an Ar-filled double glaze IGU of 1.0 W/m2K.
U-valuePerformance(W/m2K)Tvis (%)g-value (%)Product with 4% emissivity1.28066Product with 3% emissivity1.17963Product with 2% emissivity1.07053
As can be seen, the visible transmission and g-value drop at this lowest reported emissivity level. As is know, new regulations in Europe, for example, will go into effect that will require U-values even lower than 1.0 W/m2K. Conventional approaches for reducing the U-value yet further may result in unacceptable visible transmission and g-value losses and, in fact, sometimes may not even be possible or feasible in all cases.
Thus, it will be appreciated that there is a need in the art for improved window glazings that have yet further reduced U-values while still maintaining acceptable visible transmission and g-value.
In certain example embodiments of this invention, an insulating glass (IG) unit is provided. First, second, and third substantially parallel spaced apart glass substrates are provided, with the first substrate being an outermost substrate and the third substrate being an innermost substrate. A first spacer system is disposed around peripheral edges of the first and second substrates, with a first cavity being defined between the first and second substrates. A second spacer system is disposed around peripheral edges of the second and third substrates, with a second cavity being defined between the second and third substrates. First and second low-emissivity (low-E) coatings are disposed on interior surfaces of the first and third substrates respectively such that the first and second low-E coatings face one another. First and second antireflective coatings are disposed on opposing major surfaces of the second substrate. Each said low-E coating comprises, in order moving away from the substrate on which it is disposed: a layer comprising titanium oxide, a layer comprising zinc oxide, an infrared reflecting layer comprising silver, a layer comprising a metal, oxide, or sub-oxide of Ni and/or Cr, a layer comprising tin oxide, and a layer comprising silicon nitride.
In certain example embodiments of this invention, an insulating glass (IG) unit is provided. First, second, and third substantially parallel spaced apart glass substrates are provided, with the first substrate being an outermost substrate and the third substrate being an innermost substrate. First and second low-emissivity (low-E) coatings are disposed on interior surfaces of the first and third substrates respectively such that the first and second low-E coatings face one another. Each said low-E coating includes at least one Ag-based infrared (IR) reflecting layer sandwiched between one or more dielectric layers. First and second antireflective coatings are disposed on opposing major surfaces of the second substrate. The first and third substrates are heat treated and the second substrate is not heat treated.
In certain example embodiments of this invention, a method of making an insulating glass (IG) unit is provided. First, second, and third glass substrates are provided, with the second substrate supporting first and second antireflective (AR) coatings on opposing major surfaces thereof. The first substrate supports a first low-emissivity (low-E) coating on one major surface thereof, and the third substrate supports a second low-E coating on one major surface thereof. The first, second, and third substrates are oriented in substantially parallel spaced apart relation to one another using first and second spacer systems, with the first spacer system being located around peripheral edges of and spacing apart the first and second substrates, and with the second spacer system being located around peripheral edges of and spacing apart the second and third substrates. The first substrate is an outermost substrate and the third substrate is an innermost substrate. The first and second low-E coatings are disposed on interior surfaces of the first and third substrates respectively such that the first and second low-E coatings face one another. Each said low-E coating comprises, in order moving away from the substrate on which is disposed: a layer comprising titanium oxide, a layer comprising zinc oxide, an infrared reflecting layer comprising silver, a layer comprising a metal, oxide, or sub-oxide of Ni and/or Cr, a layer comprising tin oxide, and a layer comprising silicon nitride.
In certain example embodiments of this invention, a method of making an insulating glass (IG) unit is provided. A first low-emissivity (low-E) coating is disposed on a first substrate. First and second antireflective (AR) coatings are disposed on opposing major surfaces of a second substrate. A second low-E coating is disposed on a third substrate. Either (a) the first, second, and third substrates are built into an IG unit, or (b) the first, second, and third substrates are forwarded to a fabricator to be built into an IG unit. In the built IG unit, the second substrate is sandwiched between the first and third substrates such that the first and second low-E coatings face one another.
The features, aspects, advantages, and example embodiments described herein may be combined to realize yet further embodiments.